1. Field of the Invention
The present invention relates to a magnetic recording medium, method and apparatus for fabricating the medium.
2. Description of the Prior Art
Conventionally, materials for magnetic printer drums are used, for example, by thermo-magnetic printers in which a magnetic latent image is formed on a magnetic recording medium, and the latent image is developed to a visible image (see, Shunji Imamura, "Magnetography Printer", Chapter 15, pp. 159-168, of "Nonimpact printing", CMC, Japan, 1986).
FIG. 1 is a schematic view illustrating printing process of a conventional thermo-magnetic printer. In FIG. 1, a recording magnetic drum 1 rotates in the direction indicated by the arrow A. The recording magnetic drum 1 has on its surface a magnetic recording medium made from a CrO.sub.2 thin film or the like for forming a magnetic latent image thereon.
In the printing process, an erasing means 2 initially magnetizes the magnetic recording medium in a predetermined direction. Then, a magnetic recording means 3 forms a designated magnetic latent image thereon, and a development means 4 processes the latent image into a visible image by making toners adhere to the surface of the drum 1 in response to the magnetic latent image. The toners adhere to portions at which magnetic forces produced by the leakage magnetic field on the surface of the magnetic recording medium intersect the surface of the magnetic recording medium. Thus, the magnetic latent image is developed to a visible image.
Following this, a transfer means 5 and a fixing means 6 transfers and fixes the visible image on paper, respectively. Finally, a cleaning means 7 removes remaining toners from the magnetic recording means, thus completing the printing process.
The magnetic latent image can be recorded on the magnetic recording medium by using a thermal head or by irradiating a laser beam to heat the recording medium. The magnetic recording medium can be magnetized in two different directions: one mainly along the surface of the recording medium (longitudinal recording method); and the other in the direction perpendicular to the surface of the recording medium (vertical recording method), The vertical recording method is used when a high resolution is required. Magnetic recording media for the vertical recording are formed with alloy films of elements of the rare earth family and i ton family, that is, with RE-TM alloy films or Co-Cr alloy films. The RE-TM alloy films are mainly used for photomagnetic disks using a magnetic recording method, and the Co-Cr alloy films are mainly used for magnetic disks using a magnetic head recording method.
These days, thin films such as Co/Pt artificial superlattices or Co/Pd artificial superlattices, or multilayer films that overlay these artificial superlattices can be used as vertical magnetization films.
These magnetic recording media, however, have the following problems: the Co-Cr alloy films have high Curie points, and this makes it difficult to carry out the thermo-magnetic recording; the RE-TM alloy films, on the other hand, has small residual flux density, and this makes the adhesion of toners insufficient.
In addition, with regard to the Co/Pt artificial superlattices or Co/Pd artificial superlattices, although squareness ratios of the magnetic hysteresis curve thereof are unity as long as the films are extremely thin of hundreds of angstroms, the squareness ratios decline below unity when the film thickness is thousands of angstroms, which gives only insufficient residual flux density for magnetic recording. In addition, the coercivity is small, about 200 Oe. The multilayer films of the artificial superlattices, on the other hand, can be used as magnetic recording media because they have a squareness ratio of unity and coercivity of about 2,000 Oe. These films, however, are difficult to fabricate, and further, it takes long time to fabricate them.
As described above, although the thermo-magnetic printers using vertical magnetization films for vertical recording can achieve, in their principle, reliable recording with a high resolution, and can operate with small power consumption, they have the following problems: first, there is no appropriate materials for the vertical magnetization films; and second, for improving the magnetic characteristics of the recording media, the structure of films becomes complex, and hence the fabrication thereof becomes difficult.